Wet spinning of cellulose acetate



Patented Jan. 18, 1944 WET SPINNING or CELLULOSE ACETATE Francis P. Alles, Waynesboro, Va., asslgnor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing? Application August 7, 1941, Serial No. 405,888

'Claims. (CI. 18-54 Thi invention relates to the spinning of cellulose acetate filaments, and more particularly to the wet spinning of acetone-soluble cellulose acetate directly from. the gum stage.

A number of methods have heretofore been proposed for forming filaments of cellulose acetate by directly extruding the gum (i. e., theacetic acid solution of cellulose acetate produced in the customary acetylation processes) through suit able orifices and into a coagulating bath whereby to form filaments. Certain of these proposed methods are restricted to the spinning of-pri-,

to hydrolysis, it is inherently more brittle, and

it cannot be dyed satisfactorily with existing dyes. The product of these methods cannot therefore successfully compete with dry-spun yarn.

' The proposed methods which do relate tol the wet spinning of the acetone-soluble cellulose acetate likewise have not achieved commercial-sue taining not more than 15% by weight of water, based on the total weight of the solution, into a dilute aqueou solutionof aceticacidcontaining not more than 15% and not less than 5% by weight of acetic acid. The coagulating solution is maintained at a temperature of from about 3 C. to about 12 0.. The yarn is withdrawn from the coagulating solution and is subjected to the usual steps of winding, washing, drying, etc. A notable feature of my invention is that yarn issuingfrom the coagulating bath is particularly susceptible to stretch either in air or in an acetic acid stretching bath. The tenacity of the yarn is greatly enhanced by such treatment.

The following general procedur is preferred in carrying out my invention: Cellulose acetate gum-prepared by the esterification of cotton linters and hydrolyzed to obtain the desired percentage of combined acetic acid, is treated with a salt of acetic acid, for instance sodium acetate, to neutralize or render ineffective the sulfuric acid catalyst and thereby arrest further hydrolysis. The gum is then filtered to remove any undissolved material and stored in suitable tanks cess. In many instances, commercial failure; may

or it may be in the coagulating'vaction itself for v .7 of conventional design. The spinneret, preferj not all coagulants for cellulose'acetate arei-suit- I able in the spinning of acetone-soluble cellulose For example, ammonium sulfate andacetate. 7 ammonium chloride, which are *knownto be coagulants for acetone-soluble cellulose acetate, and

which have actually been'disclosed heretofore in the spinning of chloroform-soluble cellulose'acetate, are wholly unsatisfactory inthe spinning of acetone-soluble cellulose acetate because the yarns produced therefrom are'full'of stuck filas I ments and are harsh and :.wiry to the'feel' and chalky in appearance.

An object of my invention, therefore, is toprovide a method for producing high-quality spinning of acetone-soluble cellulose acetate gums. These and other objects will more clearly appear hereinafter. a

These objects are accomplished by my invention which-briefly stated, comprises spinmng a for a sufficient length of time to allow the air entrained therein to cream out. The gum, which is now ready'for spinning, isfed to a spinneret ably, is immersed justbelow the surface of the coagulating bath in such a way as to permit the filaments to be spun horizontally. After passing through a suitable guide, the yarn is withdrawn from the coagulating bath by means of positively driven rolls. The yarn may be collected on a bobbin, in a centrifugal bucket or dropped into a slowly revolving can, or the acid yarn may be cut into staple lengths and processed on a conveyor belt. If it is desired to stretch the yarn after .leaving the coagulating bath in order to obtain improved physical properties, the yarn is led to a .second set of rolls, the speed of which may be varied with. respect to the first set of rolls in order to obtain the desired degree of stretch. The yarn may be stretched in air, or, where a high degree of stretch is desired, the yarn may be passed through a tank containing acetic acid and water at a controlled temperature and then stretched. After stretching, the yarn may be collected on a bobbin or in a centrifugal bucket or slowly revolving can, or the acid yarn may be 1 cut into staple lengths and processed on a conveyor belt. The yarn may be washed in the form collected or withdrawn and washed in a counterguni of acetone-soluble cellulose acetate concurrent system a a rope or threat. The acid? ously or intermittently and sent to the recovery system.

My invention is further illustrated by the following examples. Parts are by weight unless otherwise stated.

Example I Cellulose acetate gum containing 14% (54.5%

combined acetic acid) cellulose acetate was spun through a 60-hole spinnneret hole diameter 0.003 inch, into a coagulating bath containing 5.7% acetic acid in water at 7? C. The yarn was collected on a bobbin, washed and dried. Yarn spun under these conditions was clear and had good luster. Denier per filament 7.7, tenacity 1.02 grams per denier, elongation 10.1%.

Example II Cellulose acetate gum containing 14% (54.5% combined acetic acid) cellulose acetate was spun through a 60-h01e spinneret, hole diameter 0.003

inch, into a coagulating bath containing 10% acetic acid in water at 4 C. The yarn was collected on a bobbin, then reeled into skeins, washed and dried. Denier per filament 7.9, tenacity 1.00 gram per denier, elongation 17%.

Example III A gum containing 14% cellulose acetate (56% combined acetic acid) was spun into a coagulating bath containing 12% acetic acid in water at a temperature of 6 C. A 100-hole spinneret, hole diameter 0.0025 inch, was used. The coagulated thread, after being withdrawn from the coagulating bath, was run through a bath containing 30% acetic acid at a temperature of 50 C. and stretched 60%. The wind-up speed was 3100 inches per minute. The thread was collected on a a bobbin, washed and dried. Denier per filament 2.24, tenacity 2.44 grams per denier, elongation Example IV A gum containing 11% cellulose acetate (54.5% combined acetic acid), 11% water, 77% acetic acid, and 1% sulfuric acid which had been neutralized with sodium acetate, was spun into a coagulating bath containing 10% acetic acid in water at a temperature of 9 C. The gel yarn withdrawn from the coagulating bath was then passedthrough 30% acetic acidin water at 50 C. and stretched 60%. The yarn was collected on a bobbin, Washed and dried. Final wind-up speed was 3200 inches per minute. Denier per filament 2.3, tenacity 1.7 grams per denier, elongation 3.4%.

Example V The same gum used in Example IV wasspun into a .coagulating bath containing 14% .acetic acid in water at 3 C. through a 100-hole'spinneret, hole diameter 0.0025 inch, and wound up at a speed of 3240 inches per minute. The yarn was collected on a bobbin, washed and dried.

Denier per filament 2.1, tenacity 1.4 grams per denier. elongation 4.7%.

' wash water eiliuent is preferably sent to an ex- E'xample VI The same gum used in Example IV was spun into a coagulating bath containing 14% acetic acid in water at a temperature of 3 C. An 800-hole spinneret, hole diameter 0.003 inch, was used. The yarn, after coagulation, was passed through a stretching bath of 30% acetic acid at a temperature of 45 C. and the yarn stretched 60%. The yarn in this case was not wound onto a bobbin but was dropped as a loose coil into a slowly revolving can, later reeled into skeins, washed and dried under substantially no tension. Denier per filament 1.2, tenacity 1.6 grams per denier, elongation 11% My invention is of course susceptible to wide variation from the exact conditions set out in the foregoing examples. which are for purposes of illustration only. Thus, any cellulose acetate in the acetone-soluble range having a combined acetic acid content of 50% to 57% may be employed, although the preferred acetate is one containin from 54.5% to 56% combined acetic acid.

A gum composition containing. 11% to 15% by weight of cellulose acetate is in general preferred, but a higher content is permissible if the gum is heated to reduce its viscosity. The water content of the gum should not exceed 15% based on the total weight of the solution, and is preferably maintained .within the range of 5-l0%. The small percentage of sodium, ammonium, calcium, or magnesium sulfate normally resulting from neutralization of the sulfuric acid acetylation catalyst may be retained in the gum without harmful effect.

The acetic acid content of the coagulating bath should be kept within the limits of from 5% to 15% by weight. A concentration of 12% by weight of acetic acid is preferred. Acetic acid concentrations higher than 15% result in a weak gel yarn and broken filaments. Acetic acid in concentrations lower than 5% results in chalky yarn.

It is desirable to maintain the temperature of the coagulating solution under 12 C., but not lower'than 3 C. Temperatures lower than 3 C. result in'a freezing of the gum in the spinneret. This, of-course', could be eliminated by heating the gum prior to spinning. If the temperature of the coagulating solution is raised much above 12 C., the rate of coagulation is slowed down to a point where the gel yarn is weak with resulting broken filaments. Best results are obtained when the temperature of the coagulant is maintained within the range of 5-8 C.

Yarn withdrawn from the coagulating solution may, if desired, be stretched up to 25% to 30% in air. If it is desired to stretch the yarn more than 30%, the yarn may be run through a stretching bath containing 25%, to 35% acetic acid, preferably from 25% to 30% of acetic acid, at a temperature of 35 C. to 50 C., and preferably from 40 C. to 50 C., and then stretched. In this way, it is possible to obtain up to stretch.

I claim:

1. The method of forming filaments, yarns and threads from cellulose acetate which comprises spinning a gum of cellulose acetate containing between 50% and 57% combined acetic acid, said gum containing less than 15% by weight of water, into an aqueous coagulating solution maintained at a temperature of from about 3 C. to about 12 C., said coagulating solution containing not over I 15% and not less than 5% by weight of acetic acid, andwithdrawing the formed filaments from said bath, and thereafter stretching said filaments whereby to increase their tenacity.

2. The method of forming filaments, yarns and threads from cellulose acetate which comprises spinning a gum comprising not more than 15% by weight of water and from 11% to 15% by weight of cellulose acetate containing from 54.5% to 56% combined acetic acid, into an aqueous coagulating solution maintained at a temperature of from about 3 C. to about 12 0., said coagulating solution comprising not over 15% and not less than by weight of acetic acid, and withdrawing the formed filaments from said bath. and thereafter stretching said filaments whereby toincrease-their tenaci 3. The method 01 forming filaments, yarns and threads from cellulose acetate which comprises spinning a gum comprising not more than 15% by weight of water and from 11% to 15% by weight of cellulose acetate containing from 54.5% to 56% combined acetic acid, into an aqueous coagulating solution maintained at a temperature of from about 3 C. to about 12 (1., said coagulating solution comprising not over 15% and not less than 5% by weight of acetic acid, and withdrawing the formed filaments from said bath,

s 3 and thereafter stretching said filaments whereby to increase their tenacity.

4. The method of forming filaments, yarns and threads from cellulose acetate which comprises spinning a gum comprising from about 5% to about by weight of water and from about 11% to about 15% by weight of cellulose acetate containing from 54.5% to 56% combined acetic acid, into an aqueous coagulating solution maintained at. a temperature of from 5 C. to 8 C.', said coagulating solution containing about 12% by weight of acetic acid, withdrawing the formed filaments from said solution, and thereafter stretching said filaments in an aqueous solution of acetic acid containing from to by weight of acetic acid and maintained at a temperature of from 35 C. to C. whereby to increase their tenacity.

5. In the process of spinning filaments directly from a gum ofacetone-soluble cellulose acetate. the improvement which comprises extruding said gum into an aqueous solution comprising not more than 15% and not less than5% by weight of acetic acid, said solution being maintained at a temperature or from about 3 C. to about 12 C.

FRANCIS P. ALLES. 

